Method for forming underlying insulation film

ABSTRACT

The surface of an insulating film disposed on an electronic device substrate is irradiated with plasma based on a process gas comprising at least an oxygen atom-containing gas, to thereby form an underlying film at the interface between the insulating film and the electronic device substrate. A good underlying film is provided at the interface between the insulating film and the electronic device substrate, so that the thus formed underlying film can improve the property of the insulating film.

TECHNICAL FIELD

The present invention relates to a process for forming an insulatingfilm having a good interfacial property. More specifically, the presentinvention relates to a method of irradiating an insulating film withplasma based on a process gas comprising at least an oxygenatom-containing gas, to thereby improve the interfacial property betweenthe insulating film and the substrate. The modification processaccording to the present invention is suitably usable, particularly fora so-called high-k (high-dielectric constant) material.

BACKGROUND ART

In general, the present invention is widely applicable to the productionof materials for electronic device such as semiconductors orsemiconductor devices, and liquid crystal devices. For the convenienceof explanation, however, the background art relating to semiconductordevices as an example of the electronic devices, will be described here.

Substrates for semiconductors or electronic device materials such assilicon have been subjected to various kinds of treatments such asformation of an oxide film, film formation by CVD (chemical vapordeposition), etc., and etching. According to the recent requirement forforming microstructures and attaining further development in theperformances in the field of semiconductor devices, the demand for aninsulating film having a higher performance (for example, in view ofleakage current) has been increased remarkably. This is because theleakage current of a certain degree can cause a severe problem in therecent devices which have attained finer structures, and/or higherperformances, even when the leakage current of such a degree haveactually caused substantially no problem in the conventional deviceshaving a lower degree of integration. Particularly, in view of thedevelopment in the mobile or portable-type electronic devices in aso-called “ubiquitous” society of recent construction (i.e.,information-oriented society wherein people can use a network service,anytime and anywhere, by means of electronic devices), it is necessaryto develop a low-power consumption device, and therefore the reductionin the leakage current is an extremely important issue.

Typically, in a case where the formation of a finer structure in ahigh-performance silicon LSI is pursued, for example, for the purpose ofdeveloping a next-generation MOS-type transistor, there arises herperformance a problem that the leakage current is increased and theresultant power consumption is also increased. Accordingly, in order todecrease the power consumption thereof while pursuing a higherperformance, it is necessary to improve the transistor characteristicwithout increasing the gate leakage current in the MOS-type transistor.

In order to satisfy this requirement, various techniques (for example,the modification of a silicon oxide film and the use of a siliconoxynitride film SiON) have been proposed. Among these, one usefultechnique is the development of an insulating film using a high-k(high-dielectric constant) material. This is because the use of such ahigh-k material is expected to reduce the EOT (effective oxidethickness), which is an SiO₂ capacity-equivalent film thickness.

However, when such an insulating film, which has been expected toprovide a good property, is actually formed by CVD (chemical vapordeposition method) or the like, particularly in the case of theformation of an insulating film having a very high practical utility(for example, a relatively thin insulating film of about 12 A(angstrom)), a good interfacial property can be hardly obtained betweenthe insulating film and the underlying electronic device substrate.

One promising method for solving such a problem may be to form a verythin (for example, 10 A or less) underlying film on a substrate, and toform an insulating film on the underlying film. However, it is verydifficult to form such a thin underlying film directly on an electronicdevice substrate by using a conventional thermal oxidation or plasmaoxidation technique (the thickness of a thin film can be hardlycontrolled by such a technique), while controlling the film-forming rateor in-plane uniformity.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a process for formingan underlying film, which has solved the problem encountered in theprior art.

Another object of the present invention is to provide a process capableof forming a good underlying film at the interface between an insulatingfilm and an electronic device substrate so as to improve the resultanttransistor characteristic.

As a result of earnest study, the present inventors have found that,when an insulating film (for example, high-k material film) is onceformed on an electronic device substrate and plasma based on a processgas comprising at least an oxygen atom-containing gas is caused to passthrough the insulating film so as to form an underlying film at theinsulating film-substrate interface, such a process is extremelyeffective in achieving the above-mentioned object, unlike theconventional technique wherein an underlying film is formed on anelectronic device substrate and then an insulating film (for example,high-k material film) is formed thereon.

The process for forming underlying insulating film according to thepresent invention is based on the above discovery. More specifically,the process comprises: irradiating the surface of an insulating filmdisposed on an electronic device substrate with plasma based on aprocess gas comprising at least an oxygen atom-containing gas, tothereby form an underlying film at the interface between the insulatingfilm and the electronic device substrate.

The present invention also provides an electronic device material,comprising: an electronic device substrate, an underlying film disposedon the substrate, and an insulating film disposed on the underlyingfilm,

-   -   wherein the underlying film is a film which has been formed by        supplying plasma from the insulating layer side.

In the process for forming an underlying film according to the presentinvention having such a constitution, active plasma species (forexample, oxygen reactive species) are caused to pass through theinsulating film from the insulating film surface side to reach theinsulating film-substrate interface, to thereby form an underlying filmin the vicinity of the interface. In the present invention, thefilm-forming rate can be controlled (that is, the film-forming time canbe controlled) easily, as compared with the case wherein an underlyingfilm is directly formed on an electronic device substrate. Accordingly,in the present invention, it is easy to control the thickness of theunderlying film and/or to improve the in-plane uniformity of theunderlying film.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic vertical sectional view showing an example of thesemiconductor device, which can be produced by the process for formingan underlying insulating film according to the present invention.

FIG. 2 is a schematic vertical sectional view showing an example of thesemiconductor-fabricating apparatus for practicing the process forforming an underlying insulating film according to the presentinvention.

FIG. 3 is a schematic vertical sectional view showing an example of theplane antenna (RLSA; sometimes also referred to as “slot plane antenna”or “SPA”) plasma processing unit, which is usable in the process forforming an underlying insulating film according to the presentinvention.

FIG. 4 is a schematic plan view showing an example of RLSA, which isusable in the process and apparatus for forming an underlying insulatingfilm according to the present invention.

FIG. 5 is a schematic vertical sectional view showing an example of theheating reaction furnace unit, which is usable in the process forforming an underlying insulating film according to the presentinvention.

FIG. 6 is a schematic sectional view showing an example of the siliconsubstrate on which a gate oxide film or gate insulating film is to beformed.

FIG. 7 is a schematic sectional view showing an example of the plasmaprocessing to be effected on the surface of a substrate.

FIG. 8 is a schematic sectional view showing an example of the formationof a high-k material film.

FIG. 9 is a schematic sectional view showing an example of the plasmaprocessing to be effected on a high-k material.

FIG. 10 is a schematic sectional view showing an example of theformation of a gate electrode on a high-k material film.

FIG. 11 is a schematic sectional view showing an example of theformation of an MOS capacitor.

FIG. 12 is a schematic sectional view showing an example of theformation of a source and a drain by ion implantation.

FIG. 13 is a schematic sectional view showing an example of thestructure of an MOS-type transistor, which is obtainable by the presentinvention.

FIG. 14 is a graph showing a change in the electrical film thickness(Teq) and uniformity in the electrical film thickness, with respect tothe oxidation time, when the surface of an HfSiO film and an oxide filmformed by an RLSA oxidation process is subjected to an oxidizing plasmaprocessing.

FIG. 15 is a graph showing a change in the electrical film thickness(Teq) and uniformity in the electrical film thickness, with respect tothe oxidation time, when the surface of an HfSiO film and an oxide filmformed by an RLSA oxidation process is subjected to an oxidizing plasmaprocessing.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be described in detail, withreference to the accompanying drawings as desired. In the followingdescription, “%” and “part(s)” representing a quantitative proportion orratio are those based on mass, unless otherwise specifically noted.

(Process for Forming Underlying Film)

In the present invention, the surface of an insulating film disposed onan electronic device substrate is irradiated with plasma based on aprocess gas comprising at least an oxygen atom-containing gas, tothereby form an underlying film at the interface between the insulatingfilm and the electronic device substrate.

(Insulating Film)

The material for constituting the insulating film, which is usable inthe present invention, is not particularly limited. In view of apractical MOS-type transistor, it is preferred to use one or at leasttwo materials selected from the group consisting of: SiO₂, SiON, eachhaving a low dielectric constant, SiN having a relatively highdielectric constant, and substances having a high dielectric constant,which are called a “high-k substance” as described later.

(High-k Material)

The high-k material, which is usable in the present invention is notparticularly limited. In view of the trend for an MOS-type transistor ata practical level, it is preferred to use those having a “k” (dielectricconstant) value of 8 or more, more preferably 10 or more.

Preferred examples of such a high-k material may include, one or atleast two materials selected from the group consisting of: Al₂O₃, ZrO₂,HfO₂, Ta₂O₅, silicates such as ZrSiO and HfSiO, and aluminates such asZrAlO, can be suitably used.

(Electronic Device Substrate)

The electronic device substrate which is usable in the present inventionis not particularly limited. It is possible to use one or combination ofat least two species, which are selected from the known electronicdevice substrates. Specific examples of the electronic device substratemay include a semiconductor material, a liquid crystal device material,etc. Specific examples of the semiconductor material may include:materials mainly comprising single-crystal silicon, and high performanceCMOS, etc.

(Underlying Film)

The composition, thickness, stacking or lamination form, etc., of theunderlying film are not particularly limited, as long as the interfacialproperty of the above-mentioned insulating film can be improved. In viewof transistor characteristic, the underlying film may preferably be anunderlying oxide film.

The underlying film may preferably have a thickness of about 6 to 12 A,more preferably about 6 to 8 A.

(Process Gas Conditions)

In the formation of the underlying film according to the presentinvention, the following conditions can be suitably used in view ofproperty of the underlying film to be formed.

Rare Gas (for example, Kr, Ar, He or Xe):

from 300 to 2,000 sccm, more preferably from 1,000 to 2,000 sccm

O₂: from 1 to 500 sccm, more preferably from 10 to 300 sccm

Temperature:

-   -   from room temperature (25° C.) to 500° C., more preferably from        250 to 500° C., still more preferably from 250 to 400° C.

Pressure:

-   -   from 3 to 500 Pa, more preferably from 7 to 260 Pa

Microwave:

-   -   from 1 to 5 W/CM², more preferably from 2 to 4 W/cm², still more        preferably from 2 to 3 W/cm²        (Annealing)

In the present invention, after the above-mentioned modification, theinsulating film may be subjected to annealing, as desired. Theconditions for the annealing are not particularly limited. In view ofthe transistor characteristic, a process gas containing an O₂ gas and/oran N₂ gas is suitably usable. Examples of the conditions, which aresuitably usable in the present invention, are described below.

(Suitable Annealing Conditions)

Rare Gas (for example, Kr, Ar, He or Xe):

-   -   from 0 to 5,000 sccm, more preferably from 0 to 1,000 sccm    -   O₂: from 10 to 1,000 sccm, more preferably from 10 to 100 sccm    -   N₂: from 1,000 to 5,000 sccm, more preferably from 1,000 to        3,000 sccm

Temperature:

-   -   from room temperature (25° C.) to 1,050° C., more preferably        from 600 to 1,050° C.

Pressure:

-   -   from 100 to 101 kPa, more preferably from 1 k to 101 kPa

The plasma which is usable in the present invention is not particularlylimited. It is preferred to use a high-density plasma having arelatively low electron temperature, because it may easily provide auniform thin film.

(Suitable Plasma)

The property of the plasma which is suitably usable in the presentinvention are as follows.

-   -   Electron temperature: 0.5-2.0 eV    -   Density: from 1E10 to 5E12/cm³    -   Uniformity of plasma density: ±10%        (Plane Antenna Member)

In the process for forming an electronic device material according tothe present invention, plasma having a low electron temperature and ahigh density is formed by supplying microwave via a plane antenna memberhaving a plurality of slots. In the present invention, the film isformed by using the plasma having such an excellent characteristic, andtherefore the present invention can provide a process which accomplishesa light plasma damage, and a high reactivity at a low temperature.Further, in the present invention, as compared with a case usingconventional plasma, a high-quality insulating film may easily be formedby supplying microwave via a plane antenna member.

According to the present invention, a high-quality underlying film canbe formed. Accordingly, a semiconductor device structure having anexcellent characteristic may easily be formed by forming another layer(for example, an electrode layer) on the underlying film.

(Preferred Characteristic of Underlying Film)

According to the present invention, an underlying film having thefollowing preferred characteristic can easily be formed.

(Preferred Characteristic of Semiconductor Structure)

The extent to which the process according to the present invention isapplicable is not particularly limited, but the high-quality underlyingfilm formable by the present invention can suitably be used,particularly as a gate insulator constituting an MOS structure.

(Preferred Characteristic of MOS Semiconductor Structure)

The very thin underlying film having a good quality, which is formableby the present invention, can suitably be used particularly as aninsulating film constituting a semiconductor device (particularly, as agate insulator constituting an MOS semiconductor structure).

According to the present invention, an MOS semiconductor structurehaving the following preferred characteristic can easily be produced.When the characteristic of the insulating film which has been modifiedby the present invention may be evaluated, for example, by a methodwherein a standard MOS semiconductor structure as described in apublication (see, Masanori Kishino and Mitsumasa Koyanagi, “VLSI Deviceno Butsuri (Physics of VLSI Devices)”, pp. 62-63, published by Maruzen)is fabricated and the evaluation of the characteristic of the thusfabricated MOS can be used as the evaluation of the characteristic ofthe insulating film itself. This is because, in such a standard MOSstructure, the characteristic of the insulating film constituting theMOS structure has much effect on the MOS characteristic.

One Embodiment of Production Apparatus

One preferred embodiment of the production process according to thepresent invention is described below.

First, as an example of the structure of a semiconductor device whichcan be produced by the process for producing an electronic devicematerial according to the present invention, a semiconductor devicehaving an MOS structure having a gate insulator as the insulating filmis described below, with reference to FIG. 1.

Referring to FIG. 1( a), the reference numeral 1 in this FIG. 1( a)denotes a silicon substrate, numeral 11 denotes a field oxide film,numeral 2 denotes a gate insulator and numeral 13 denotes a gateelectrode. Referring to FIG. 1( b), this gate insulator 2 comprises anunderlying oxide film 21 and a high-k substance 22. As described above,the production process according to the present invention may provide avery thin underlying oxide film 21 having a good quality.

In this example, it is preferred that the high-quality underlying oxidefilm 21 comprises a silicon oxide film (hereinafter referred to as “SiO₂film”) which has been formed by irradiating a substrate to be treatedmainly comprising Si, with a microwave through a plane antenna memberhaving a plurality of slots in the presence of a process gas comprisingO₂ and a rare gas so as to generate plasma, and forming the oxide filmat the surface between the high-k substance and the substrate by usingthe thus generated plasma. When such underlying SiO₂ is used, asdescribed hereinafter, it is easy to obtain a good Si/gate insulatorinterfacial property (such as interfacial level), and a good gateleakage characteristic.

One Embodiment of Production Process

Next, the process for producing such an electronic device materialcomprises a gate insulator 2 and a gate electrode 13 is described below.

FIG. 2 is schematic view (schematic plan view) showing an example of thetotal arrangement of a semiconductor manufacturing equipment 30 forconducting the process for producing an electronic device materialaccording to the present invention.

As shown in FIG. 2, in a substantially central portion of thesemiconductor manufacturing equipment 30, there is disposed atransportation chamber 31 for transporting a wafer W (FIG. 2). Aroundthe transportation chamber 31, there are disposed: plasma processingunits 32 and 33 for conducting various treatments on the wafer, two loadlock units 34 and 35 for conducting the communication/cutoff between therespective processing chambers, a heating unit 36 for operating variousheating treatments, and a heating reaction furnace 47 for conductingvarious heating treatments on the wafer. These units are disposed so asto surround the transportation chamber 31. Alternatively, it is alsopossible to provide the heating reaction furnace 47 independently andseparately from the semiconductor manufacturing equipment 30.

On the side of the load lock units 34 and 35, a preliminary cooling unit45 and a cooling unit 46 for conducting various kinds of preliminarycooling and cooling treatments are disposed.

In the inside of transportation chamber 31, transportation arms 37 and38 are disposed, so as to transport the wafer W (FIG. 3) between theabove-mentioned respective units 32-36.

On the foreground side of the load lock units 34 and 35 in this figure,loader arms 41 and 42 are disposed. These loader arms 41 and 42 can putwafer W in and out with respect to four cassettes 44 which are set onthe cassette stage 43, which is disposed on the foreground side of theloader arms 41 and 42.

In FIG. 2, as the plasma processing units 32 and 33, two plasmaprocessing units of the same type are disposed in parallel.

Further, it is possible to exchange both of the plasma processing units32 and 33 with a single-chamber type CVD process unit, It is possible toset one or two of such a single-chamber type CVD process unit in theposition of plasma processing units 32 and 33.

When two plasma processing units 32 and 33 are used, it is possible thatan oxidizing treatment is conducted in the plasma processing unit 32,and a nitriding treatment is conducted in the plasma processing unit 33.Alternatively, it is also possible that the oxidizing treatment and thenitriding treatment are conducted in parallel, in the plasma processingunits 32 and 33.

One Embodiment of Plasma Processing Apparatus

FIG. 3 is a schematic sectional view in the vertical direction showingthe plasma processing unit 32 (or 33) which is usable in the filmformation of the gate insulator 2.

Referring to FIG. 3, reference numeral 50 denotes a vacuum containermade of, e.g., aluminum. In the upper portion of the vacuum container50, an opening portion 51 is formed so that the opening portion 51 islarger than a substrate (for example, wafer W). A top plate 54 in a flatcylindrical shape made of a dielectric such as quartz and aluminumnitride so as to cover the opening portion 51. In the side wall of theupper portion of vacuum container 50 which is below the top plate 54,gas feed pipes 72 are disposed in the 16 positions, which are arrangedalong the circumferential direction so as to provide equal intervalstherebetween. A process gas comprising at least one kind of gas selectedfrom O₂, inert gas, N₂, H₂, etc., can be supplied into the vicinity ofthe plasma region P in the vacuum container 50 from the gas feed pipes72 evenly and uniformly.

On the outside of the top plate 54, there is provided a radio-frequencypower source, via a plane antenna member 60 having a plurality of slots,which comprises a plane antenna (RLSA) made from a copper plate, forexample. As the radio-frequency power source, a waveguide 63 is disposedon the top plate 54, and the waveguide 63 is connected to a microwavepower supply 61 for generating microwave of 2.45 GHz, for example. Thewaveguide 63 comprises a combination of: a flat circular waveguide 63A,of which lower end is connected to the RLSA 60; a circular waveguide63B, one end of which is connected to the upper surface side of thecircular waveguide 63A; a coaxial waveguide converter 63C connected tothe upper surface side of the circular waveguide 63B; and a rectangularwaveguide 63D, one end of which is connected to the side surface of thecoaxial waveguide converter 63C so as to provide a right angletherebetween, and the other end of which is connected to the microwavepower supply 61.

In the inside of the above-mentioned circular waveguide 63B, an axialportion 62 of an electroconductive material is coaxially provided, sothat one end of the axial portion 62 is connected to the central (ornearly central) portion of the RLSA 60 upper surface, and the other endof the axial portion 62 is connected to the upper surface of thecircular waveguide 63B, whereby the circular waveguide 63B constitutes acoaxial structure. As a result, the circular waveguide 63B isconstituted so as to function as a coaxial waveguide.

In addition, in the vacuum container 50, a stage 52 for carrying thewafer W is provided so that the stage 52 is disposed opposite to the topplate 54. The stage 52 contains a temperature control unit (not shown)disposed therein, so that the stage can function as a hot plate.Further, one end of an exhaust pipe 53 is connected to the bottomportion of the vacuum container 50, and the other end of the exhaustpipe 53 is connected to a vacuum pump 55.

One Embodiment of RLSA

FIG. 4 is a schematic plan view showing an example of RLSA 60 which isusable in an apparatus for producing an electronic device materialaccording to the present invention.

As shown in this FIG. 4, on the surface of the RLSA 60, a plurality ofslots 60 a, 60 a, . . . are provided in the form of concentric circles.Each slot 60 a is a substantially square penetration-type groove. Theadjacent slots are disposed perpendicularly to each other and arrangedso as to form a shape of alphabetical “T”-type character. The length andthe interval of the slot 60 a arrangement are determined in accordancewith the wavelength of the microwave supplied from the microwave powersupply unit 61.

One Embodiment of Heating Reaction Furnace

FIG. 5 is schematic sectional view in the vertical direction showing anexample of the heating reaction furnace 47 which is usable in anapparatus for producing an electronic device material according to thepresent invention.

As shown in FIG. 5, a processing chamber 82 of the heating reactionfurnace 47 chamber is formed into an air-tight structure by usingaluminum, for example. A heating mechanism and a cooling mechanism areprovided in the processing chamber 82, although these mechanisms are notshown in FIG. 5.

As shown in FIG. 5, a gas introduction pipe 83 for introducing a gasinto the processing chamber 82 is connected to the upper central portionof the processing chamber 82, the inside of the processing chamber 82communicates with the inside of the gas introduction pipe 83. Inaddition, the gas introduction pipe 83 is connected to a gas supplysource 84. A gas is supplied from the gas supply source 84 into the gasintroduction pipe 83, and the gas is introduced into the processingchamber 82 through the gas introduction pipe 83. As the gas in thiscase, it is possible to use one of various gas such as raw material forforming a high-k insulating film such as HTB and silane, for example. Asdesired, it is also possible to use an inert gas as a carrier gas.

A gas exhaust pipe 85 for exhausting the gas in the processing chamber82 is connected to the lower portion of the processing chamber 82, andthe gas exhaust pipe 85 is connected to exhaust means (not shown) suchas vacuum pump. Due to the exhaust means, the gas in the processingchamber 82 is exhausted through the gas exhaust pipe 85, and theprocessing chamber 82 is maintained at a desired pressure.

In addition, a stage 87 for carrying the wafer W is provided in thelower portion of the processing chamber 82.

In the embodiment as shown in FIG. 5, the wafer W is carried on thestage 87 by means of an electrostatic chuck (not shown) having adiameter which is substantially the same as that of the wafer W. Thestage 87 contains a heat source means (not shown) disposed therein, tothereby constitute a structure wherein the surface of the wafer W to beprocessed which is carried on the stage 87 can be adjusted to a desiredtemperature.

The stage 87 has a mechanism which is capable of rotating the wafer wcarried on the stage 87, as desired.

In FIG. 5, an opening portion 82a for putting the wafer W in and outwith respect to the processing chamber 82 is provided on the surface ofthe right side of the processing chamber 82 in this figure. The openingportion 82 a can be opened and closed by moving a gate valve 98vertically (up and down direction) in this figure. In FIG. 5, atransportation arm (not shown) for transporting the wafer is providedadjacent to the right side of the gate valve 98. In FIG. 5, the wafer Wcan be carried on the stage 87, and the wafer W after the processingthereof is transported from the processing chamber 82, as thetransportation arm enters the processing chamber 82 and goes outtherefrom through the medium of the opening portion 82 a.

Above the stage 87, a shower head 88 as a shower member is provided. Theshower head 88 is constituted so as to define the space between thestage 87 and the gas introduction pipe 83, and the shower head 88 isformed from aluminum, for example.

The shower head 88 is formed so that the gas exit 83 a of the gasintroduction pipe 83 is positioned at the upper central portion of theshower head 88. The gas is introduced into the processing chamber 82through gas feeding holes 89 provided in the lower portion of the showerhead 88.

Embodiment of MOS Transistor Formation

Hereinbelow, there is described a preferred example of the processwherein an MOS-type transistor comprising a wafer W having thereon aninsulating film 2 comprising a high-k insulating film 22 and anunderlying oxide film 21 is formed by using the above-mentionedapparatus.

FIGS. 6 to 13 are schematic views each showing an example of each stepin the process according to the present invention.

Referring to FIG. 6, a field oxide film, a channel implant and asacrificial oxide film are formed on the wafer W surface so as toprovide an element isolation (or device isolation) in a previous step.The.

Subsequently, a gate valve (not shown) provided at the side wall of thevacuum container 50 in the plasma processing unit 32 (FIG. 3) is opened,and the above-mentioned wafer Was shown in FIG. 8, from which thesacrificial oxide film has been removed, is placed on the stage 52 (FIG.3) by means of transportation arms 37 and 38.

Next, the gate valve was closed so as to seal the inside of the vacuumcontainer 50, and then the inner atmosphere therein is exhausted by thevacuum pump 55 through the exhaust pipe 53 so as to evacuate the vacuumcontainer 50 to a predetermined degree of vacuum and a predeterminedpressure in the container 50 is maintained. On the other hand, microwave(e.g., of 2 W/cm²) is generated by the microwave power supply 61, andthe microwave is guided by the waveguide so that the microwave isintroduced into the vacuum container 50 via the RLSA 60 and the topplate 54, whereby radio-frequency plasma is generated in the plasmaregion P of an upper portion in the vacuum container 50.

Herein, the microwave is transmitted in the rectangular waveguide 63D ina rectangular mode, and is converted from the rectangular mode into acircular mode by the coaxial waveguide converter 63C. The microwave isthen transmitted in the cylindrical coaxial waveguide 63B in thecircular mode, and transmitted in the circular waveguide 63A in theexpanded state, and is emitted from the slots 60 a of the RLSA 60, andpenetrates the plate 54 and is introduced into the vacuum container 50.In this case, microwave is used, and accordingly high-density plasma canbe generated. Further, the microwave is emitted from a large number ofslots 60 a of the RLSA 60, and accordingly the plasma is caused to havea high density.

In advance of the introduction of the microwave, the step of FIG. 7(nitridation treatment before the formation of a high-k film) isperformed by introducing a rare gas such as krypton or argon, which is aprocess gas for the formation of an oxide film, and an N₂ gas from thegas supply tube 72 at a flow rate of, for example, 1,000 sccm and 40sccm, respectively, while heating the wafer W, for example, at 400° C.by controlling the temperature of the stage 52. When this treatment isconducted, the substrate silicon can be prevented from reacting with ahigh-k substance at the formation of the high-k film to form a siliconoxide film at the interface therebetween.

Then, the wafer is set in a heat treatment unit 47. In this heattreatment unit 47, a film of a high-k substance is formed on the upperpart of the wafer W. For example, in a case where a film of hafniumsilicate (HfSiO) is formed on the silicon substrate W, tertiary ethoxyhafnium (HGB: Hf(OC₂H₅)₄) and a silane gas (SiH₄) are introduced at 1sccm and 400 sccm, respectively, and the pressure is kept at 50 Pa. Theflow rate of HGB is the flow rate of a liquid mass-flow controller andthe flow rate of the silane gas is the flow rate of a gas mass-flowcontroller. In this atmosphere, the above-mentioned silicon substrate isheated at 350° C. and the reactive species Hf, Si and O are reacted onthe substrate to form an HfSiO film. By controlling the processconditions including the treatment time, an HfSiO film of 4 nm is formed(FIG. 8).

Thereafter, a gate valve (not shown) is opened and transportation arms37 and 38 (FIG. 2) are introduced into the vacuum container 47 so thatthey receive the wafer W. The transportation arms 37 and 38 take out thewafer W from the heat treatment unit 47 and then set the wafer on thestage in the plasma processing unit 33.

Embodiment of Nitride-Containing Layer Formation

Subsequently, as shown in FIG. 11, the surface of the wafer W issubjected to an oxidation treatment in the plasma processing unit 33,and an underlying oxide film 21 (FIG. 1( b)) is formed on the bottomsurface of the previously formed high-k insulating film 2.

At the formation of this underlying oxide film, the conditions in thevacuum container 50, for example, are set such that the wafertemperature is, for example, 400° C. and the process pressure is, forexample, 133 Pa (1 Torr), and an argon gas and an O₂ gas are introducedinto the container 50 from the gas introduction pipe at a flow rate of,for example, 2,000 sccm and 200 sccm, respectively.

At the same time, a microwave of, for example, 2 W/cm² is generated froma microwave power supply 61 and this microwave is guided by a wave-guidepath and introduced into the vacuum container 50 through the RLSA 60 band the top plate 54, whereby high-frequency plasma is generated in theplasma region P in the upper region of the vacuum container 50.

In this process (the formation or the underlying oxide film), the gasintroduced is converted into plasma to form oxygen radials, and the thusformed oxygen radials transmit through the high-k substance and reactwith the silicon substrate, to thereby form an SiO₂ film at theinterface between the high-k substance and the silicon substrate. Inthis way, as shown in FIG. 1( b), the underlying oxide film 21 is formedat the interface between the high-k substance 22 and the siliconsubstrate 1 on the wafer W.

Embodiment of Gate Electrode Formation

Then, a gate electrode 13 (FIG. 1( a)) is formed on the wafer, on whichthe high-k substance and the underlying oxide film have been formed(FIG. 10). This gate electrode is formed in a heat treatment unit of thesame type as shown in FIG. 5. This heat treatment unit is sometimesinstalled integrally with the semiconductor production apparatus 30shown in FIG. 2, or the treatment is sometimes performed in a separateapparatus.

At this time, the treatment conditions can be selected according to thekind of the gate electrode 13 to be formed.

More specifically, in a case where a gate electrode 13 comprisingpolysilicon is formed, the treatment is preformed by using, for example,SiH₄ as the process gas (electrode-forming gas) under the conditionssuch that the pressure is from 10 to 500 Pa and the temperature is from580 to 680° C.

In a Case where a gate electrode 13 comprising amorphous silicon isformed, the treatment is preformed by using, for example, SIH₄ as theprocess gas (electrode-forming gas) under the conditions such that thepressure is from 10 to 500 Pa and the temperature is from 500 to 580° C.

(Quality of Oxide Film)

In the above-mentioned step of FIG. 11, at the time of the formation ofan underlying oxide film for the gate underlying film, plasma containingoxygen (O₂) and rare gas is formed by supplying microwave on the wafer Wmainly comprising Si through a plane antenna member (RLSA) in thepresence of a process gas, and by using the thus formed plasma, an oxidefilm is formed on the surface of the substrate to be treated, so thatthe oxide film can have a high quality and the film quality can besuccessfully controlled.

Thereafter, patterning and selective etching for a gate are performed toform an MOS capacitor (FIG. 11), and the resultant product is thensubjected to ion implantation to form a source and a drain (FIG. 12).Subsequently, the dopant (for example, phosphorus (P), arsenic (As) andboron (B), etc., which have been implanted into the channel, source anddrain) is activated by annealing, and then the resultant product issubjected to a wiring step as a post step by combining interlayerinsulating film formation, patterning, selective etching and metal filmformation. In this way, an MOS-type transistor according to thisembodiment is obtained (FIG. 13). Finally, the upper part of theresultant transistor is subjected to a wiring step by using variouspatterns to form a circuit, to thereby complete a logic device.

In this embodiment, Hf silicate (HfSiO film) is formed as the insulatingfilm, but an insulating film having another composition may also eformed. As for the gate insulating film, it is possible to use one ormore kinds selected from the group consisting of; SiO₂, SiON, eachhaving a low dielectric constant, which have been heretofore used, SiNhaving a relatively high dielectric constant, Al₂O₃, ZrO₂, HfO₂, Ta₂O₅,each having a high dielectric constant, which are called a high-ksubstance, silicates such as ZrSiO and HfSiO, and aluminates such asZrAlO.

In addition, only the thermal CVD process is described as a practicalexample of the film-formation process for the high-k substance, but anarbitrary process may be used for the film formation of the high-ksubstance. For example, the film formation can be also performed byplasma CVD or PVD process.

Further, in this example, only the effect by the plasma oxidationtreatment is noted, but the present invention is also applicable to, forexample, plasma nitridation treatment, or a treatment comprising acombination of plasma oxidation treatment and plasma nitridationtreatment, instead of the plasma oxidation treatment.

Hereinbelow, the present invention will be described in more detail withreference to Examples.

EXAMPLES Example 1

FIG. 14 and FIG. 15 show a change in the electrical film thickness (Teq)and in the uniformity of the electrical film thickness (range:difference between the maximum and minimum values of in-plane Teq),respectively, with respect to the oxidation time, when an oxidizingplasma processing is applied onto the HfSiO film and the oxide filmformed by an RLSA oxidation process. Samples as shown in FIGS. 14 and 15were produced by the following process.

(1) Substrate

A p-type silicon substrate having a resistivity of 8 to 12 Ωcm and aplane direction of (100) was used as the substrate. On the surface ofthe silicon substrate, a 500 A-sacrificial oxide film was formed by athermal oxidization process.

(2) Pretreatment for HfSiO Film Formation

The sacrificial oxide film and contaminant factors (metals, organicmaterials and particles) were removed by RCA washing using a combinationof APM (a mixed solution of ammonia, aqueous hydrogen peroxide and purewater), HPM (a mixed solution of hydrochloric acid, aqueous hydrogenperoxide and pure water) and DHF (a mixed solution of hydrofluoric acidand pure water). The chemical concentration ratio of the APM wasNH₄OH:H₂O₂:H₂O=1:2:10 and the temperature was 60° C. The concentrationratio of the HPM was HCl:H₂O₂:H₂O1:1:5 and the temperature was 60° C.The concentration ratio of the DHF was HF:H₂O=1:9 and the temperaturewas 23° C. In the treatment, APM: 10 minute→pure water rinsing: 5minutes→DHF: 23 minutes→pure water rinsing: 5 minutes→HPM: 10minute→pure water rinsing: 5 minute→final pure water rinsing: 10 minuteswere performed. Thereafter, IPA (isopropyl alcohol, 220° C.) drying wasperformed for 9 minutes to dry the water content on the wafer. Theresulting substrate was kept at 700° C. and kept for 1 minute in anatmosphere (atmospheric pressure) where NH₃ was introduced at 2,000sccm, to thereby form a thin nitride layer (SiN layer) on the substratesurface. Due to the formation of the SiN layer, the silicon substrateand the HfSiO film can be prevented from a thermal reaction.

(3) HfSiO Film Formation

On the silicon substrate in the above (2), a hafnium silicate (HfSiO)film was formed. Tertiary ethoxy hafnium (HTB: Hf(OC₂H₅)₄) and silanegas (SiH₄) were introduced at 1 sccm and 400 sccm, respectively, and thepressure was kept at 50 Pa. The flow rate of HGB was the flow rate of aliquid mass-flow controller and the flow rate of silane gas was the flowrate of a gas mass-flow controller. In this atmosphere, the siliconsubstrate in the above (2) was heated at 350° C. and the reactivespecies Hf, Si and O were reacted oh the substrate to form an HfSiOfilm. By controlling the process conditions including the treatmenttime, an HfSiO film of 4 nm was formed.

(4) RLSA Oxidation Treatment

The silicon substrate treated in the above (3) step was then subjectedto an RLSA plasma oxidation treatment. On the silicone substrate heatedat 400° C., a rare gas and oxygen were flown at 2,000 sccm and 200 sccm,respectively, and the pressure was kept at 67 Pa (500 mTorr). In thisatmosphere, microwave of 2.8 W/cm² was supplied through a plane antennamember (RLSA) to form plasma containing oxygen and rare gas, and byusing the thus formed plasma, a plasma oxidation treatment was appliedonto the substrate in the above (3).

(5) TiN Film Formation for Gate Electrode

On the HfSiO film which had been formed through (3) and (4) steps and asa reference, on an oxide film which had been formed by performing onlythe oxidation treatment of (4) but omitting the HfSiO film formation of(3), a titanium nitride (TiN) film was formed as a gate electrode by aCVD process. The silicon substrate which had been treated in the above(3) and (4) steps was heated at 550° C. and under a pressure of 200 Pa,TiCl₄ gas, NH₃ gas and N₂ gas were introduced on the substrate at 30sccm, 100 sccm and 150 sccm, respectively, whereby a 800 A-thick TiNfilm for an electrode was formed on the HfSiO film.

(6) Patterning, Gate Etching

The TiN electrode which had been formed in the above (5) step wassubjected to patterning by lithography and then, the silicon substratewas soaked in an aqueous hydrogen peroxide (H₂O₂) chemical solution for90 minutes to dissolve the TiN in the non-patterned portion, to therebyform an MOS capacitor.

Example 2

The Cv property of the MOS capacitor which had been produced in Example1 was evaluated. This measurement was performed by the followingprocess. The CV property was evaluated for a capacitor having a gateelectrode area of 10,000 μm². The CV property was determined byevaluating the capacitance at each voltage in the process of sweepingthe gate voltage from 1 V to about −2 V at a frequency of 1 MHz. Fromthe thus determined CV property, the electrical film thickness wascalculated.

FIG. 14 shows an electrical film thickness (Teq) when an oxidizingplasma processing is applied onto the HfSiO film and the oxide filmformed by an RLSA oxidation process. The abscissa indicates an oxidationtreatment time and the ordinate indicates an electrical film thickness(Teq).

As shown in FIG. 14, the reference oxide film reaches a film thicknessof 25 A when the oxidation time is 20seconds or more. As the treatmenttime is shorter, the reproducibility of the process becomes lower, andthe control of the film thickness also becomes more difficult.Therefore, a short-time process of 20 seconds or less is not practical.This reveals that the film thickness (10 A or less) to be required as ahigh-k oxynitride film can be hardly obtained by the normal oxidationprocess as shown in the reference of FIG. 14 . On the other hand, whenthe RLSA oxidation treatment is applied to an HfSiO film as shown inFIG. 14, even if a long-time treatment of 35 seconds or more is applied,the increase in the electrical film thickness is as small as about 10 A,based on the initial film thickness (about 16 A). Only a rare gas and anoxygen gas are used for the oxidation process, and therefore it isconsidered that this film thickness increase is attributable to oxygen.It is considered that the film thickness increase may include the filmthickness increase from the interface and the film thickness increase inthe film itself (hulk). At present, crystallization due tohigh-temperature annealing is known as a problem of the high-k substanceincluding HfSiO film. This crystallization is considered to occur due toa small absolute amount of Si atoms in the film. In this meaning, thefilm thickness increase resulting from the mingling or mixing of oxygeninto the film is unlikely the film thickness increase resulting from theinsertion of O atoms into the Si—Si bonds. Also, as is known in general,the Hf—O bonds are abundantly contained. From these, the matter mostgreatly contributing to the film thickness increase may highly probablybe the film thickness increase from the substrate, that is, theformation of an oxide film at the interface. Accordingly, it isconsidered that a very thin oxide film can be formed at the interface bythe present invention.

FIG. 15 shows a change in the uniformity of the electrical filmthickness (range: difference between the maximum and minimum values ofin-plane Teq) when an oxidizing plasma processing is applied onto theHfSiO film and the oxide film formed by the RLSA oxidation process. Theabscissa indicates the oxidation treatment time and the ordinateindicates the range.

As shown in FIG. 15, in a case where the reference RLSA oxide film, therange value is less changed with respect to the treatment time, but whenthe RLSA oxidation treatment is applied to the HfSiO film, the rangebecomes smaller, that is, the uniformity is further improved, as thetreatment time is increased. The mechanism therefor is considered asfollows. When the film thickness increase is mainly due to the formationof the oxide film at the interface as described above, a strongthickness increase effect is provided in the thin portion of film and aweak thickness increase effect is provided in the thick portion of film.Therefore, it can be considered that the non-uniformity in the filmthickness is improved by applying RLSA oxidation and a uniformelectrical film thickness is obtained. The results of FIG. 15 cansupport the above-mentioned mechanism of film thickness increase in FIG.14.

As understood from the above, by applying plasma oxidation treatmentafter forming an HfSiO film, a very thin underlying film of 10 A or lesscan be realized, although such a thickness has been difficult to berealized by an oxidation process of a simple substance, and at the sametime, an HfSiO film having a good uniformity can be formed.

In the above Examples, only an HfSiO film produced by using the presentinvention is referred to, but the same effect can be obtained byapplying the same treatment to other high-k substances.

INDUSTRIAL APPLICABILITY

As described hereinabove, the present invention can provide a process ofproviding a good underlying film at the interface between an insulatingfilm and an electronic device substrate, so that the thus formedunderlying film can improve the property of the insulating film.

1. A method for forming an insulating film, comprising: plasma nitridinga surface of a substrate before formation of a high-dielectric constantinsulating film, forming a high-dielectric constant insulating film onthe substrate, generating plasma based on a process gas comprising atleast an oxygen atom-containing gas on the high-dielectric constantinsulating film, irradiating the surface of the high-dielectric constantinsulating film with the plasma to thereby form an oxide film at theinterface between the high-dielectric constant insulating film and thesubstrate, and nitriding the surface of the high-dielectric constantinsulating film after formation of the oxide film, wherein the oxidefilm has a thickness of 6-12 Å.
 2. A method for forming an insulatingfilm according to claim 1, wherein the plasma is generated based onmicrowave via a plane antenna member (RLSA) having a plurality of slots.3. A method for forming an insulating film according to claim 1, whereinthe high-dielectric constant insulating film comprises at least onematerial selected from the group consisting of Al₂O₃, ZrO₂, HfO₂, Ta₂O₅,ZrSiO, HfSiO and ZrAlO.
 4. A method for forming an insulating filmaccording to claim 1, wherein the process gas comprises at least onerare gas selected from the group consisting of Kr, Ar, He and Xe,wherein the oxygen atom-containing gas is O₂ gas.
 5. A method forforming an insulating film according to claim 1, further comprisingannealing the substrate after the formation of the oxide film, whereinthe annealing is conducted at a temperature of 500-1100° C.
 6. A methodfor forming an insulating film according to claim 5, wherein theannealing is conducted in an atmosphere of N₂, O₂, or N2 and O₂.
 7. Amethod for forming an insulating film, comprising: plasma nitriding asurface of a substrate before formation of a HfSiO film on thesubstrate, forming a HfSiO film on the substrate, generating plasmabased on a process gas comprising at least an oxygen atom-containing gason the HfSiO film, and irradiating the surface of the HfSiO film withthe plasma, to thereby form an oxide film at the interface between theHfSiO film and the substrate, wherein the oxide film has a thickness of6-12 Å.
 8. A method for forming an insulating film according to claim 7,wherein the oxygen atom-containing gas is O₂ gas and the process gascomprises at least one rare gas selected from the group consisting ofKr, Ar, He and Xe.
 9. A method for forming an insulating film accordingto claim 7, further comprising annealing the substrate after formationof the oxide film, wherein the annealing is conducted at a temperatureof 60-1100° C.
 10. A method for forming an insulating film according toclaim 9, wherein the annealing is conducted in an atmosphere of N₂, O₂,or N2 and O₂.
 11. A method for forming an insulating film according toclaim 7, wherein the substrate is at a temperature from room temperatureto 500° C., wherein the oxide film is formed at a pressure of 3-500 Pa.12. A method for forming an insulating film according to claim 7,wherein the HfSiO film is formed by using tertiary ethoxy hafnium (HTB:Hf(OC₂H₅)₄) and silane gas (SiH₄).
 13. A method for forming aninsulating film according to claim 7, further comprising washing thesubstrate before the formation of the HfSiO film.
 14. A method forforming an insulating film, comprising: plasma nitriding a surface of asubstrate before formation of a HfSiO film, forming a HfSiO film on thesubstrate, generating plasma based on a process gas comprising at leastan oxygen atom-containing gas on the HfSiO film, irradiating the surfaceof the HfSiO film with the plasma to thereby form an oxide film at theinterface between the HfSiO film and the substrate, and nitriding thesurface of the HfSiO film, wherein the oxide film has a thickness of6-12 Å.
 15. A method for forming an insulating film according to claim14, further comprising washing the substrate before the formation of theHfSiO film.
 16. A method for forming an electronic device, comprising:forming a high-dielectric constant gate insulating film on a substrate,generating plasma based on a process gas comprising at least an oxygenatom-containing gas on the high-dielectric constant gate insulatingfilm, irradiating a surface of the high-dielectric constant gateinsulating film with the plasma, to thereby form an oxide film at theinterface between the high-dielectric constant gate insulating film andthe substrate, nitriding the surface of the high-dielectric constantgate insulating film after formation of the oxide film, and forming agate electrode on the high-dielectric constant gate insulating film,wherein the oxide film has a thickness of 6-12 Å.
 17. A method forforming an electronic device according to claim 16, further comprisingannealing the surface of the high-dielectric constant gate insulatingfilm after the formation of the oxide film.
 18. A method for forming anelectronic device according to claim 16, wherein the high-dielectricconstant gate insulating film comprises at least one material selectedfrom the group consisting of Al₂O₃, ZrO₂, HfO₂, Ta₂O₅, ZrSiO, HfSiO andZrAlO.
 19. A method for forming an electronic device according to claim16, further comprising plasma nitriding the surface of the substratebefore the formation of the high-dielectric constant gate insulatingfilm.